The Dissipative Particle Dynamics model is specially attractive for the simulation of complex fluids like colloidal suspensions, polymers, amphiphilic systems, etc, because its extreme simplicity and flexibility. However, it suffers from a basic conceptual problem which is the lack of a well-defined scale. A calibration process is always needed in DPD. In this talk, we show that the model can be improved by introducing the concept of fluid particles with a definite size. Issues like the resolution of the DPD simulation (i.e. the scale at which we are resolving flows) have sense in this improved model closely related to the Smoothed Particle Hydrodynamics model. We also show that the original DPD equations emerge naturally in the process of a semi rigorous coarse-graining (in terms of blobs) the microscopic detail of big spherical molecules.